This disclosure relates to a cutting insert, in particular a tangential cutting insert, for a tool for machining a workpiece. Furthermore, the disclosure relates to a tool for machining a workpiece, in particular for tangential milling, having a tool holder which has at least one cutting-insert receptacle in which a cutting insert according to the present disclosure is releasably fastened.
Cutting inserts of the present type, which are generally denoted indexable cutting inserts or in particular as tangential cutting inserts, are usually used in applications for metalworking, in particular in milling or turning applications. Primarily, the present cutting inserts are used for tangential milling. Milling tools in which such cutting inserts are used typically comprise a rotationally symmetrical tool holder on the circumference of which at least one, but usually a multiplicity of said cutting inserts are releasably fastened.
The removal of material from the workpiece during the milling operation is ensured by high-precision blade edges or cutting edges which are formed in the cutting inserts. In order to keep the wear as low as possible, to withstand the very high cutting forces that arise during processing and to ensure precision that is as high as possible, these cutting inserts are usually produced from carbide. Nevertheless, on account of the high material stress, the cutting edges become worn over time. Therefore, in particular for milling operations which require high precision, the cutting inserts have to be replaced after a particular period of time.
In order to prevent the relatively expensive cutting inserts from having to be replaced in their entirety each time the cutting edges become worn, multisided cutting inserts which have a plurality of cutting edges that are arranged in a symmetrical manner with respect to one another have been developed. Such an indexable cutting insert having four identical main cutting edges that are arranged in a symmetrical manner with respect to one another is known for example from EP 1 572 407 B1.
The indexable cutting insert shown therein is formed so as to be rotationally symmetrical through 180° with regard to each of its three main axes. As soon as the used main cutting edge becomes worn, the indexable cutting insert can therefore be rotated and/or reversed through 180° and be fastened in the new position in the tool holder. In the event of wear to one of the four main cutting edges, the indexable cutting insert thus does not have to be replaced in its entirety but only rotated or reversed in the holder, and so machining can be continued with the previously unused, unworn main cutting edges.
On account of the symmetry properties of the indexable cutting insert, in which each main cutting edge has the same cutting edge geometry, the cutting properties are not changed by reversing or rotating the indexable cutting insert. In other words, one and the same indexable cutting insert can thus be used four times until all of the cutting edges become worn and the indexable cutting insert has to be disposed of.
In contrast to simple, non-reversible cutting inserts, such indexable cutting inserts afford much greater flexibility and, since they are usable repeatedly, can be used for much longer without this being associated with losses in terms of machining accuracy. Although such four-edged indexable cutting inserts are much more complex to produce than conventional, single-edged (non-reversible) cutting inserts, they prove to be not only more versatile but also, when considered as a whole, more cost-effective for the consumer.
However, from the point of view of the manufacturer of such indexable cutting inserts, the problem in structural terms is not only that of realizing the symmetry properties of such indexable cutting inserts with a plurality of identical cutting edges, but at the same time also ensuring that each of these cutting edges has the same machining properties and as a result is usable in an identical manner. The greatest problem is in this case often that of avoiding possible collisions with other components of the cutting insert or of the tool holder, and of ensuring secure seating of the cutting insert in the tool receptacle of the tool holder, so that optimal force introduction is ensured.
In particular, care must be taken to ensure that the cutting edges that are not being used at the particular time or other components of the cutting insert do not collide in an undesired manner with the workpiece. Thus, collisions with the workpiece must not occur at locations on the cutting insert which are not intended to be used for machining the workpiece at the particular time. In other words, care must thus be taken to ensure that the cutting edges that are not being used at the particular time run free. It stands to reason that such requirements are more difficult to meet in the case of indexable cutting inserts having a plurality of alternately usable cutting edges than is the case for conventional cutting inserts having only one cutting edge.
The abovementioned symmetry properties, the free running of the remaining cutting edges and the avoidance of undesired collisions of the cutting insert with the workpiece is solved in the case of the indexable cutting insert known from EP 1 572 407 B1 in that the indexable cutting insert has two parts which are twisted through a predefined angle with respect to one another about a main axis of the indexable cutting insert. The main cutting edges are in this case each twisted through a predefined angle with respect to one another. In this way, the required symmetry and free-running properties can be ensured in a technically sustainable manner. On the other hand, in the case of such an indexable cutting insert that is twisted on itself, a relatively large number of surfaces of complex shape arise. Such twisting results, in particular at the main insert surfaces, in relatively complex rake faces which are technically very demanding to manufacture. Demanding manufacture of this type, even if this should be technically feasible, is associated with very high manufacturing costs. Ultimately, this results in high unit costs of the indexable cutting inserts for the final consumer.